Currently, a recording/reproducing device for recording digital information (data) on a portable recoding medium such as an optical disk or magneto-optical disk, and reproducing digital information from the recording medium is widely used. In a recording/reproducing device for recording information in a DVD-RAM using laser beams, for example, a plurality of marks and spaces having different lengths are formed on an optical disk according to data to be recorded. The marks and spaces formed on the optical disk are read using laser beams, whereby the data is reproduced.
However, even when data is written using laser beams having the same laser power or pulse waveform, shapes of marks formed on the recording medium may vary due to individual differences between devices and between recording media. If the shape of the mark is deviated from a desired shape, the waveform of a read reproduction signal is deviated from an original waveform, resulting in degradation of reproduction quality. Thus, the recording/reproducing device has a problem such that the quality of a reproduction signal when data recorded on the recording medium is reproduced may significantly vary depending on the device or the recording medium.
For preventing such deterioration in reliability of the reproduction signal, test recording is conducted in loading a recording medium in the recording/reproducing device or in doing other operations. Specifically, predetermined data is recorded in a predetermined area on the recording medium, and this recorded data is reproduced to check signal quality. Based on the results, the recording/reproducing device optimizes the characteristics of a reproduction system, and optimizes a parameter for recording (recording parameter).
It is to be noted that, in this specification, the recording parameter means, in a broad sense, a parameter specifying a recording operation of the device, capable of changing the shape of a mark formed on the recording medium. Typically, the recording parameter is a parameter specifying the waveform of a recording pulse that is used when an optical disk or the like is irradiated with a laser beam (e.g. pulse width, pulse edge position, etc.).
Particularly, in a recording medium in which information is recorded by heat resulting from irradiation of a laser beam such as an optical disk, a mark having an undesired shape (i.e. mark shifted in edge position) is easily formed due to heat interference. The degree of the heat interference varies depending on the pattern of marks and spaces formed on the recording medium. Therefore, if such a recoding medium is used, an optimum parameter is preferably set according to the above pattern.
In test recording, the quality of the reproduction signal is determined based on, for example, jitter (swing of reproduction signal along the direction of the time axis). FIG. 1 shows a conventional optical disk drive 900 optimizing the characteristics of the reproduction system or the recording parameter so that the jitter of the reproduction signal is minimized.
The optical disk drive 900 has an optical head 2 for writing information on an optical disk 1 or reading information from the optical disk 1. When data is read, reflection of light irradiated onto the optical disk 1 (reflected light) is converted into a reproduction signal matching the recorded data in the optical head 2.
The reproduction signal is waveform-shaped by a waveform equalizer 3, and then binarized by a comparator 4. The threshold (slice level) of this comparator 4 is feedback-controlled by an integration circuit or the like (not shown) so that the integral of a binarized output from the comparator 4 equals 0. This is because a recording method such that the integral of a reproduction signal equals 0 is usually employed, and undesired variations in the reproduction signal caused by external factors (e.g. variations in reflectivity of the recording medium, etc.) are inhibited taking advantage of the fact that the reproduction signal ideally has no direct current components (i.e. DC free).
Then, in a phase comparator 5, a phase difference between the binarized output from the comparator 4 and a reproduction clock signal is measured. The reproduction clock signal is extracted from clock information included in a reproduction signal by a PLL (phase locked loop) circuit. More specifically, the phase difference detected in the phase comparator 5 is averaged by an LPF (low-pass filter) 6, and this is used as a control voltage of a VCO (voltage-controlled oscillator) 7. At this time, the oscillation frequency of the VCO 7 and the phase of the outputted signal are feedback-controlled so that the cumulative amount of the phase difference outputted from the phase comparator 5 equals 0. Consequently, a reproduction clock signal synchronized with the reproduction signal is outputted from the VCO 7.
However, even when a reproduction clock signal generated using the PLL circuit, there arises a phase difference between the binarized signal and the reproduction clock signal if an undesired deviation (shift) exists in the edge of a formed mark, and the length of the mark is not ideal length. In the optical disk drive 900, the jitter of the reproduction signal is measured based on this phase difference. The operation for correcting the recording parameter in the optical disk drive 900 will be more specifically described below.
First, a record compensation circuit 9 generates a recording pulse signal according to an initialized recording parameter and a predetermined recording pattern outputted from a pattern generation circuit 8. Using this recording pulse signal, a laser drive circuit 10 records data matching the predetermined recording pattern on the optical disk 1.
Then, a track on the optical disk 1 in which the data is recorded is read. At this time, a difference detection circuit 11 receives from the phase difference comparator 5 a phase difference between the output of the comparator 4 (binarized signal) and the output of the VCO 7 (reproduction clock signal), and integrates the absolute value of the phase difference. In this way, the difference detection circuit 11 integrates the absolute value of the phase difference to measure a value (jitter amount) having a correlation with the jitter, and outputs the value.
The reason why the absolute value of the phase difference is integrated in this way is that the jitter represents a degree of spread of deviation (variation) in the reproduction signal. Thus, for obtaining a value having a correlation with the jitter, a phase difference should be added while ignoring signs (polarity).
Based on the jitter amount obtained in this way, the optical disk drive 900 can determine whether the recording parameter used is appropriate or not. A large jitter amount detected means that the recording parameter is not appropriate.
In addition, for optimizing the recording parameter, the optical disk drive 900 repeats the above described operation while changing the value thereof. Consequently, a jitter amount matching each recording parameter is detected. Among these parameters, a recording parameter allowing the jitter amount to be minimized is selected to optimize the recording parameter.
The procedure for optimizing the recording parameter based on measurement of the jitter of the reproduction signal will be described in detail below with reference to FIGS. 2 and 3. A procedure will be described as an example below in which by carrying out test recording using a recording pattern specified by a 6T space, a 4T mark, a 6T space and a 8T mark, a recording parameter specifying the position of an edge behind the 4T mark (hereinafter referred to as a trailing edge) is optimized. It is to be noted that, in this specification, if the polarity inversion period (pulse width) of a recording pattern matching a mark or space formed on the recording medium is mT (m is an integer of 1 or greater, and T is a clock period), the mark or space may be referred to as an mT mark or mT space. In addition, because the above polarity inversion period mT corresponds to the length of the mark or space, the length of the mark and the length of the space may be expressed by mT in this specification.
In the optical disk 1, a shift in mark edge by heat interference is hard to occur if a long mark and space of 6T or greater is continuously formed, and for the set of a long mark and space of 6T or greater, an optimum recording parameter common in each set is already set. Specifically, in this example, recording is performed with an optimum recording parameter for a mark leading edge in the 6T space and 8T mark, or mark trailing edge in the 8T mark and 6T space.
When a periodic NRZI (non-return to zero inverted) signal (recording pattern) shown in FIG. 2(a) is given from the pattern generation circuit 8, and a predetermined recording parameter is given from an optical disk controller 12, then the record compensation circuit 9 generates, for example, a laser driving signal (recording pulse signal) as shown in FIG. 2(b). Here, the Tsfp shown in FIG. 2(b) is a recording parameter determining a position of an edge ahead of a mark (hereinafter referred to as leading edge), and the Telp is a recording parameter determining a position of a mark trailing edge. A recording pulse signal is generated based on such recording parameters.
By irradiating the optical disk 1 with a laser beam according to the recording pulse signal generated in this way, a mark is physically formed on the optical disk 1 as shown in FIG. 2(c). In the optical disk 1 using a phase change medium layer as a recording layer, this mark is formed as an amorphous area in a recording layer.
Here, consider the case where the value of Telp as a recording parameter determining the position of the trailing edge of the 4T mark is changed to Telp 1, Telp 2 and Telp 3, respectively. Furthermore, Telp 1, Telp2 and Telp 3 each correspond a width of last pulse of multi pulses for writing a 4T mark, and meet the relation of Telp 1<Telp 2<Telp 3. In addition, Telp 2 is an optimum recording parameter allowing the mark to have a desired shape. In the case where the recording parameter Telp is changed to Telp 1, Telp 2 and Telp 3 in this way, the shape of the 4T mark formed on the optical disk (position of mark trailing edge) is changed as shown in FIG. 2(c).
If the recording parameter Telp is set to an optimum value Telp 2, a reproduction signal denoted by the solid line in FIG. 2(d-1) is obtained. Furthermore, in FIG. 2(d-1), the dashed line denotes a reproduction signal when Telp is set to Telp 1 or Telp 3.
When the reproduction signal denoted by the solid line in FIG. 2(d-1) is obtained as described above, and then the threshold Th1 of the comparator 4 is set based on the reproduction signal so that the integral of the binarized output equals 0. Binarization is performed using the threshold Th1 set in this way, whereby a binarized signal is obtained. Furthermore, a phase difference between the binarized signal outputted from the comparator 4 and the reproduction signal is detected in the phase comparator 5, and the reproduction clock signal is feedback-controlled so that the integral of the detected phase difference equals 0. In this way, the reproduction clock signal shown in FIG. 2(e-1) is generated.
On the other hand, if the recording parameter Telp is set to Telp 1 being a value smaller than the optimum value Telp 2, the reproduction signal denoted by the solid line in FIG. 2(d-2) is obtained. In this case, the edge position of the 4T mark trailing edge is shifted in the direction of the time axis, and therefore the threshold Th2 of the comparator 4 is higher than the level Th1 shown in FIG. 2(d-1) as shown in FIG. 2(d-2). Consequently, the binarized signal outputted from the comparator 4 is changed. In addition, the reproduction clock signal generated so that the integral of the phase difference between itself and the binarized signal is more advanced in shift than the clock signal shown in FIG. 2(e-1) as shown in FIG. 2(e-2).
Conversely, if the recording parameter Telp is set to telp3 being a value larger than the optimum value Telp 2, the reproduction signal denoted by the solid line in FIG. 2(d-3) is obtained. In this case, the edge position of the 4T mark trailing edge is shifted in the direction of the time axis, and therefore the threshold Th3 of the comparator 4 is lower than the level Th1 shown in FIG. 2(d-1) as shown in FIG. 2(d-3). Consequently, the binarized signal outputted from the comparator 4 is changed. In addition, the reproduction clock signal generated so that the integral of the phase difference between itself and the binarized signal is less advanced in shift than the clock signal shown in FIG. 2(e-1) as shown in FIG. 2(e-3).
Here, when a shift in time or phase difference (so called inter-data clock jitter) between the reproduction signal (here binarized signal outputted from comparator) and the reproduction clock signal in the mark trailing edge (rise edge of reproduced binarized signal) is measured, distributions shown in FIGS. 3(f1) to 3(f3) are obtained when the recording parameter Telp is set to Telp 1 to Telp 3, respectively. Furthermore, a curve showing a distribution of the phase difference related to the 4T mark trailing edge and a curve showing a distribution of the phase difference related to the 8T mark trailing edge are shown in each of FIGS. 3(f1) to 3(f3). In addition, the variation in the 4T mark trailing edge and the variation in the 8T mark trailing edge are assumed to have normal distributions of the same distributed values.
FIG. 3(f-2) shows the recording parameter Telp being set to an appropriate value Telp 2. In this case, the distribution of the phase difference between the rise edge of the reproduction signal representing the 4T mark trailing edge and the reproduction clock is a normal distribution with 0 at a center, and the average value of this phase difference equals 0. Also, the distribution of the phase difference between the rise edge of the reproduction signal representing the 8T mark trailing edge and the reproduction clock is a normal distribution with 0 at a center, and the average value of this phase difference equals 0. That is, the both distribution curves are formed in such a manner that one is superimposed on another. In this way, if the recording parameter specifying the position of the trailing edge of the 4T mark is appropriate, the total jitter of the reproduction signal is minimized.
However, if the recording parameter Telp is Telp1 (value smaller than the optimum value Telp 2), the phase of the reproduction clock signal is shifted compared to the phase shown in FIG. 2(e-1) as shown in FIG. 2(e-2), and therefore neither the average value of the phase difference related to the 4T mark trailing edge nor the average value of the phase difference related to the 8T mark trailing edge equals 0 as shown in FIG. 3(f-1). Each of the distributions of these phase differences is not overlapped on another, and is a normal distribution having a center at the same distance from 0. That is, the phase of the reproduction clock is changed due to the shift in the 4T mark trailing edge, and therefore the average of the phase difference (peak of distribution curve) in either the signal matching the 4T mark or the signal matching the 8T mark recorded with an essentially appropriate recording parameter no longer equals 0. As a result, compared to the case of FIG. 3(f-2), the degree of deviation of the reproduction signal from the clock signal increases as a whole, and thus the jitter of the reproduction signal is increased.
Similarly, if the recording parameter Telp is Telp 3 (value larger than the optimum vale Telp 2), neither the average value of the phase difference related to the 4T mark trailing edge nor the average value of the phase difference related to the 8T mark trailing edge equals 0 as shown in FIG. 3(f-3). Each of the distributions of these phase differences is not superimposed on another, and is a normal distribution having a center at the same distance from 0. Furthermore, two distribution curves shown in FIG. 3(f-3) and two distribution curves shown in FIG. 3(f-1) are different in that the distribution for the 4T mark trailing edge and the distribution for the 8T mark trailing edge change their places. In this case, the spread of deviation of the reproduction signal from the clock signal increases compared to FIG. 3(f-2), and thus the overall jitter of the reproduction signal is increased.
For inhibiting the increase in jitter, the optical disk drive 900 shown in FIG. 1 accumulates the absolute value of the phase difference between the reproduction signal and the clock signal to determine a value having a correlation with the jitter, and selects a recording parameter so that the value is minimized. FIG. 3(g) is a graph showing a relation between the set recording parameter Telp and the jitter amount outputted from the difference detection circuit 11 (i.e. cumulative absolute value of phase difference). As apparent from this graph, the jitter amount outputted from the difference detection circuit 11 is minimized when the recording parameter Telp is Telp 2. The optical disk drive 900 changes the recording parameter Telp to write predetermined data for finding out such an optimum recording parameter Telp 2.
Although the procedure for optimizing the recording parameter Telp for the 4T mark trailing edge has been described in the above example, a recording pattern same as that described above (i.e. repeated pattern of 6T space, 4T mark, 6T space and 8T mark) can be used to determine an optimum value for a recording parameter Tsfp specifying a 4T mark leading edge, as well.
Furthermore, for marks of lengths other than those described above, an optimum recording parameter is determined using a similar procedure. In this case, however, test recording is carried out using a specific recording pattern matching each set of mark lengths and space lengths. For example, using a recording pattern formed by repetition of a 6T space, a 3T mark, a 6T space and a 9T mark, a recording parameter related to the 3T mark trailing edge in the set of the 3T mark and 6T space, and a recording parameter related to the 3T mark leading edge in the set of the 6T space and 3T mark are optimized.
The recording parameter set for each set of a mark length and a space length will be more specifically described below.
In the optical disk device, the polarity inversion period of a recording signal is limited to a predetermined period according to a code demodulating system or the like. That is, the lengths of marks and spaces formed on the recording medium are limited to within a predetermined range. For example, if 8/16 modulation is employed as a code modulating system, data to be recorded is represented by a recording pattern having an inversion period of 3T to 11T that is an integral multiple of a clock period T, and an SYNC code recorded for detection of synchronization is represented by a recording pattern having an inversion period of 14T. Based on this recording pattern, a mark or space having a length corresponding to the inversion period of 3T to 11T or 14T is formed on the recording medium. In this specification, this is expressed such that a mark or space having a length of 3T to 11T or 14T is formed.
Here, the minimum polarity inversion interval of a recording data signal is mT, and the maximum polarity inversion interval is nT (m and n are each an integer of 1 or greater). In this case, the lengths of a formed mark and space are expressed by mT to nT. Furthermore, the value of m (or n) may be different for the mark and the space, but the same value is adopted for both cases here.
In this case, the position of the leading edge of a mark formed on the recording medium can be changed depending on the length of the space just before the mark and the length of the mark itself. Therefore, the recording parameter Tsfp specifying the position of the leading edge is set for each set of the length mT to nT of the space just before the mark and the length mT to nT of the mark itself. In addition, the recording parameter Telp related to the mark terminal position is set for each set of the length mT to nT of the mark itself and the length mT to nT of the space just after the mark.
As described above, however, an edge shift of a mark is hard to occur in a set of a relatively long mark and a relatively long space. Thus, it is not necessary to specify a recording parameter for each set for a set of a mark and a space each having a predetermined length or greater. The predetermined length of the mark is (m+a)T, and the predetermined length of the space is (m+b)T (a and b are each an integer of 0 to n-1). In this case, the position of the leading edge of a mark formed on the recording medium can be changed depending on the set of the width mT˜(m+b)T of the space just before the mark and the length mT˜(m+a)T of the mark itself. In addition, the position of the trailing edge of a mark formed on the recording medium can be changed depending on the set of the length mT to (m+a)T of the mark itself and the width mT to (m+b)T of the space just after the mark.
Thus, the recording parameter is preferably specified for each set of one of a different mark lengths, one of b different space lengths, and one of the mark leading edge and mark trailing edge (each of a×b×2 sets).
If m=3 and a=b=3 hold, then 32 different recording parameters are specified as shown in Table 1 (recording parameter Tsfp specifying the mark leading edge) and Table 2 (recording parameter Telp specifying the mark trailing edge). This matches the specification of DVD-RAM disk having a recording capacity of 4.7 GB that is now widely used.
TABLE 1Tsfp3Tm4Tm5Tm6Tm3Ts54214Ts54215Ts54226Ts6432
TABLE 2Telp3Tm4Tm5Tm6Tm3Ts91010114Ts91010115Ts9910106Ts891010
Furthermore, in Tables 1 and 2 described above, the mark of 3T is abbreviated as “3Tm”, for example, and the space of 3T is abbreviated as “3Ts”, for example. In addition, the values in Tables are illustrative of recording parameters. In this way, the optical disk drive 900 optimizes each of 32 different recording parameters for the mark leading edge and the mark trailing edge specified for each set of a mark length and a space length.
The operation of the optical disk drive 900 in the case of optimizing all recording parameters will be described below with reference to the flowchart of FIG. 4.
First, as shown in step S1, the optical head 1 is moved (jumped) to a test recording area of the recording medium. The optical disk drive 900 carries out test recording in this area to optimize each of a plurality of recording parameters individually specified for each set of a mark length and a space length and depending on the mark leading edge or mark trailing edge.
Then, as shown in step S2, whether a recording parameter that has not optimized yet exists or not is determined, and if such a parameter exists, optimization for the parameter is carried out.
For this optimization, test recording is carried out using a recording pattern associated with the recording parameter. In test recording, recording is performed based on a predetermined recording pattern selected as a recording pattern matching the recording parameter while the value of the recording parameter is changed for each area (e.g. sector) (step S3). Consequently, a mark having a different edge position depending on the value of the recording parameter is formed in each area.
Then, data recorded in the test recording area is reproduced, and the jitter amount outputted from the difference detector 5 is measured for each area in which data is recorded while the value of the recording parameter is changed (step S4). Consequently, the relation between the value of the recording parameter and the jitter is recognized so that the optical disk drive 900 can select as an optimum value the value of a recording parameter allowing the jitter to be minimized (step S5). In this way, the recording parameter is optimized.
Then, in step S2, if there exists a recording parameter to be further optimized, optimization for the recording parameter is carried out in the same manner as described above. By repeating this operation, all recording parameters can be optimized.
In this way, in the conventional correction operation, optimization for the recording parameter is performed by selecting a parameter value allowing the jitter to be minimized from a plurality of parameter values for all recording parameters. In this case, however, test recording with different parameter values should be carried out each time each recording parameter is optimized. This is because the relation between the parameter value and the jitter shown in FIG. 3(g) must be recognized for determining a parameter value allowing the jitter to be minimized, and for this purpose, the jitter should be measured for each case where a plurality of recording parameter values are used. However, in the case where test recording using a plurality of parameter values is carried out for every recording parameter, in this way, a problem arises such that an amount of time required for the correction operation is increased.
In addition, when the jitter is measured as described above, test recording is carried out using different recording parameters according to recording parameters. Each recording pattern should be configured to make it possible to make an evaluation on whether a predetermined recording parameter is appropriate or not from the detected jitter. Accordingly, for the recording pattern, a relatively simple pattern such as a pattern formed by repletion of a 6T space, 4T mark, a 6T space and 8T mark, for example, is used so as not to match a larger number of recording parameters.
However, if such a recording patter is used, the patter of marks and spaces formed on the optical disk becomes poor in randomness. If such a regular pattern is formed, a subsequent test recording operation or the like in which a mark and a space are formed in the same area can easily be influenced by the previously formed pattern. Thus, if a pattern as described above is formed, a primary recording operation should be carried out using a random pattern before recording (overwrite) of new data is performed. This also increases an amount of time required for the test recording operation.
In this way, in the conventional method, a relatively large amount of time is required for optimizing each recording parameter. This correction operation is carried out at the time when the recording medium is attached or detached or the like, but it takes long time, and therefore a considerable amount of time is required until the device puts itself into a standby state.
The present invention has been made for solving the above problems of the conventional technique, and its object is to provide a recording/reproducing device capable of optimizing recording parameters in shorter time.